1. Field of Invention
The present invention relates to a laser technology, and more particularly to a single-shot pulse contrast measuring device.
2. Description of Related Arts
High-intensity femtosecond chirped pulse amplification (CPA) system has achieved great development, however, it still faces several important challenges, one of which is how to obtain a high enough prepulse contrast. Currently, the focused intensity of the high-power laser has reached 1022 W/cm2. To prevent the prepulses from generating the pre-plasma, it is required that the prepulse contrast of the laser pulse is at least larger than 1011:1. With further increasing the focused intensity of the laser, the demand for the pulse contrast is further improved. It challenges not only the pulse cleaning technology but also the pulse measurement technology.
The measurement of the pulse contrast is mainly based on the nonlinear correlating technology, where a pulse under test and a clean sampling pulse (e.g., second harmonic) are made cross-correlation in the form of sum frequency generation (SFG) or differential frequency generation (DFG) in the nonlinear crystal, and the contrast of the pulse under test can be obtained by measuring the dependence of the third harmonics or the idler on temporal delay. The clean sampling light is often generated by the second harmonic generation (SHG) of the pulse under test. Currently, in the scanning measurement, the dynamic range reaches 1011, and the commercial product appears. However, because most high-intensity CPA systems are operating at a very low pulse repetition rate, and even nonrepetitively, it is necessary to develop the single-shot pulse contrast measuring technology.
In the single-shot pulse contrast measuring device, time-to-space encoding must be employed to create a definite temporal window, and also a multielement detector capable of parallel detecting will be usually required, both resulting in a worse performance compared with the scanning measuring device. For the single-shot pulse contrast measuring device, the temporal window, the dynamic range and the resolution are three most important specifications. However, it is difficult for these three specifications to simultaneously meet the demands presently. For example, using the methods such as pulse front end tilting resulted from a grating and a train of discrete sampling pulse generated via Fabry-Perot etalon, the temporal window of the single-shot measurement can reach 200 ps. However, due to the limitation of the detectors, the dynamic range of these devices is only 106-107, which can not meet the actual requirements.